1. Field of the Invention
The present invention relates generally to crash cushions and terminals used in highway applications to mitigate and preclude injuries to occupants of errant vehicles.
2. Description of the Related Art
Roadway crash cushions are widely used to absorb impacts and decelerate impacting vehicles in a controlled manner. Typically, crash cushions are positioned to shield fixed objects located within the roadway environment. Crash cushions are often positioned in front of obstacles such as concrete columns and abutments. Also, crash cushions are often located at the end of a guardrail installation to prevent the upraised end of the guardrail from spearing an impacting vehicle.
There are numerous crash cushion designs known that rely upon frangible members, or members that are intended to shatter or be destroyed upon impact, to absorb the energy associated with a vehicular impact. Examples are found in U.S. Pat. Nos. 3,768,781 issued to Walker et al. and 3,982,734 issued to Walker (both employing energy cells having internal frangible members of e.g., vermiculite). One problem with the use of frangible members is the crash cushion must be completely replaced after each collision. Thus, time and expense is incurred in replacing the frangible members.
A number of previous crash cushion designs rely upon the permanent deformation of plastics or steels to absorb the kinetic energy of errant impacting vehicles. A design of that nature suffers from the same drawbacks as those designs incorporating frangible members. The cost and time associated with replacing or repairing the deformed portions of the cushion is significant.
There have been a few attempts to provide reusable or restorable crash cushions. However, for the most part, these attempts have proven impractical or unworkable in practice. U.S. Pat. No. 4,452,431 issued to Stephens et al, for instance, describes a crash cushion wherein fluid filled buffer elements are compressed during a collision. It is intended that energy be absorbed as the fluid is released from the buffer elements under pressure. In practice, it is difficult to maintain the fluid-filled cylinders as they are prone to loss of fluid through evaporation, vandalism and the like. Also, after a severe impact, holes or punctures may occur in the buffer elements rendering them incapable of holding fluid.
U.S. Pat. No. 4,674,911 issued to Gertz describes a pneumatic crash cushion that is intended to be reusable. This crash cushion employs a plurality of air chambers and valve members to absorb and dissipate impact energy. This arrangement is relatively complex and prone to failure. In addition, the numerous specialized components used in its construction make it expensive.
The Reusable Energy Absorbing Crash Terminal (“REACT”) 350 is a crash cushion wherein a plurality of polyethylene cylinders are used to absorb impact energy. The cylinders are retained within a framework of side cables and supporting frames. This system is effective and reusable to a great degree due to the ability of the cylinders to restore themselves after impact. The cylinders typically return to 85%–90% of their original shape after impact. Unfortunately, the REACT system is also expensive to construct. The number of manufacturers producing large diameter polyethylene cylinders is limited and, as a consequence, prices for the cylinders are elevated.
An improvement that addresses the problems of the prior art would be desirable.